Our long-term objectives are to quantify relationships among diet and blood amino acid (AA) concentrations associated with specific alterations in brain, liver, and muscle AA pools and changes in food intake and choice. Individual objectives are to determine: 1) quantitative relationships among diet and blood AA concentrations that lead to competition among groups of AA for uptake into tissues and result in predictable changes in tissue, especially brain, AA and neurotransmitter pools; 2) relationships between changes in brain and other tissue AA pools and in feeding behavior; 3) influences of dietary and hormonal treatments on these relationships. Rats will receive diets containing specific competitors for transport of AA; tissue AA concentrations will be determined in order to measure in vivo relationships between diet and specific changes in tissue AA pools. Neurotransmitter concentrations will be measured where selective changes occur in concentrations of brain AA precursors of neurotransmitters. Food intake/choice will be monitored (computerized system) under conditions known to alter brain or liver AA pools. Competition for AA transport into skeletal muscle will be examined in vitro in soleus muscle. Rats with lesions of the area postrema will be used to test if dietary AA may depress food intake because of malaise (learned aversions). Plasma CCK and GH will be determined in rats fed different amounts of protein. Vagotomized rats will be used to test if diet-induced depressions in food intake may be related to changes in liver AA which provides a signal via the vagus. Brain protein synthesis will be examined in vitro in an already developed system; effects of selective changes in brain AA pools on protein synthesis will be studied. Results will contribute to knowledge of regulation of tissue AA concentrations and how these may be modified selectively. Such information is essential for: 1) optimizing treatments for hepatic, renal, and genetic diseases causing impairment of AA regulatory systems; 2) understanding significance of abnormal blood AA patterns observed during use of enteral or parenteral preparations; 3) providing basic information for understanding and developing treatments for patients with behavioral aberrations and for assessing the validity of claims for effects of diet on behavior of "normal" individuals.